CBN is the hardest material next to diamond, and a sintered body prepared from the same is applied to various cutting tools. Japanese Patent Laying-Open No. 53-77811 (1978) discloses an example of such a CBN sintered body suitable for cutting tools.
The sintered body disclosed in the above prior art contains 80 to 40 percent by volume of CBN and has a remainder mainly formed of a carbide, nitride, boride or silicide of a transition metal belonging to the group IVa, Va or VIa of the periodic table or a mixture or solid solution compound thereof, with addition of Al and/or Si. In this CBN sintered body, the aforementioned compound forms continuous bonding phases in the structure of the sintered body.
In the aforementioned hard sintered body for tools, a bonding compound is prepared from a carbide, nitride, boride or silicide of a transition metal belonging to any of the groups IVa, Va or VIa of the periodic table or a solid solution compound thereof. Since such a compound has an excellent thermal conductivity and a high hardness, the sintered body generally exhibits a high performance when the same is used in a cutting tool.
However, when the sintered body which is disclosed in Japanese Patent Laying-Open No. 53-77811 (1978) and now on the market, is used for a high-speed cutting of steel, for example, so-called crater wear develops depending on the cutting conditions, to relatively shorten the life of the cutting tool.